This invention relates to electromagnetic projectile launchers and more particularly to such launchers which utilize projectile launching rails having controlled cross sectional shapes to improve projectile accelerating forces.
Parallel rail electromagnetic launchers which utilize a single pair of projectile rails require very high currents to achieve projectile velocities in excess of those obtained with conventional accelerating means such as explosives. In order to achieve a given accelerating force with a lower current, various augmentation schemes have been proposed. External augmentation is accomplished by placing additional conductors outside of the bore to increase bore flux and thereby increase the force exerted for a given current level on the armature, or on a sabot by a plasma. Internally augmented launchers have additional conductors disposed along the interior of the bore. For a given number of conductor pairs, internal series augmentation results in the highest force increase for a given current or yields the greatest current reduction for a given propelling force compared to a simple parallel rail launcher. Thus internal series augmentation is highly desirable from high propellant force and current reduction considerations. However, when the rail pairs in an internally augmented launcher are electrically connected in series, the integrity of the individual rail and armature current loops must be maintained since failure to do so will result in shorting out loops which will cause a drastic reduction in the projectile accelerating force. Because of high velocities and high currents, relatively high voltage differences exist between adjacent rails and adjacent but distinct current paths across the armature. Therefore, successful operation of internally series augmented launcher configurations is most likely to be attained for lower velocity, large bore massive projectile applications involving current conducting armatures or specially constructed sabots for plasma separation. A commonly assigned, copending application Ser. No. 381,603, filed May 24, 1982 and entitled "Parallel Rail Electromagnetic Launcher With Multiple Current Path Armature", U.S. Pat. No. 4,485,720 discloses series connected internally augmented launchers with plasma separating sabots and is hereby incorporated by reference.
The potential difference between adjacent conductors in an internally augmented launcher can be minimized through the use of multiple sources of current wherein each pair of conductors and the associated conductive armature path or plasma are supplied by an independent current source. If current is supplied by individual and presumably identical current sources to each of a number of physically in parallel projectile rail pairs, then the total current for this rail configuration is roughly, for the same overall configuration, current density and acceleration, identical to the current for a simple parallel rail launcher. Internally augmented launchers having multiple current sources are also disclosed in the above U.S. Pat. No. 4,485,720.
In a parallel rail electromagnetic launcher, a force accelerates a current carrying conductor located in a magnetic field and this force is equal to the vector cross product of the current density and the magnetic flux density. It can be shown that this force is equal to 1/2 L'I.sup.2 where L' is the inductance gradient of the parallel rail configuration and I is the current. The magnetic field, which interacts with and therefore accelerates a current carrying conducting armature or plasma, is primarily produced by the conducting rails just in the wake of the armature. For example, the magnetic field is produced by the time dependent current distribution which exists in the rails not more than roughly three bore widths behind the armature. The accelerating force is similarly a function of that instantaneous current distribution in the conducting rails right in the vicinity of the armature or driving plasma. Therefore it should be understood that the significant value of L' is the inductance gradient existing in the current conducting rails right behind or in the close vicinity of the armature. Simple parallel rail launchers of the prior art have used rectangular cross section projectile launching rails and designs have been proposed wherein the bore is circular and the rails are then essentially formed from annular sectors. Additional rail configurations improvements have been shown in commonly assigned copending application Ser. No. 571,609, filed Jan. 17, 1984 and entitled " Electromagnetic Launchers With Improved Rail Configurations". Application Ser. No. 571,609 provides additional background information and is hereby incorporated by reference.